The overall goal of this proposal is to develop widely applicable methods for non-invasive imaging of key molecular-biological and cellular events that could be useful in the assessment and management of patients with cancer and other diseases. We propose to develop technologies to image the activities of MAP kinase, Akt, and hypoxia/HIFlalpha-mediated signal transduction pathways in xenograts and transgenic brain tumor models. The regulation of these signaling pathways will be assessed at the level of transcriptional regulation using non-invasive fluorescence, bioluminscence, and positron emission tomographic imaging of GFP, luciferase, and HSVI-tk reporter gene expression, respectively. To achieve this goal, we combine established methods for non-invasive imaging of GFP, luciferase, and HSVI-tk reporter gene expression with existing molecular-biological methods that utilize reporter genes for the assessment of activities of different signal transduction pathways. We will assess the role of certain key oncogenic proteins within each of these signaling pathways. The active forms of these oncogenic proteins will be genetically introduced into transgenic animals that carry the MAP kinase, Akt, and hypoxia/HIFlalpha reporter systems. The activity of these pathways in developing gliomas will be imaged noninvasively, before and during therapy with specific inhibitors. In addition, we will test the applicability and sensitivity of different reporter gene imaging technologies to monitor changes in the activities of MAP kinase, Akt, and hypoxia/HIFlalpha-mediated signal transduction pathways in response to specific inhibitors of Mek (PD98059) and mTOR (CCI-779). We will also assess the role of Id gene expression in hypoxia/HIF1 alpha-mediated neo-angiogenesis. We will perform pilot clinical studies to assess whether HSV1-tk expression in human brain tumors can be imaged by PET after direct Adv-HSVtk injection. These pilot studies represent the "first step" to developing more advanced reporter gene imaging studies in patients with brain tumors, such as those described above.